docs: def on_basic_return(self, _channel, method, properties, body):
          """Invoke a registered callback or log the returned message.
  
          :param _channel: The channel the message was sent on
          :type _channel: pika.channel.Channel
          :param pika.spec.Basic.Return method: The method object
          :param pika.spec.BasicProperties properties: The message properties
          :param str, unicode, bytes body: The message body
  
          """
          if self.on_return:
              self.on_return(method, properties, body)
          else:
              LOGGER.critical(
                  '%s message %s published to %s (CID %s) returned: %s',
                  method.exchange, properties.message_id,
                  method.routing_key, properties.correlation_id,
                  method.reply_text)